Cellular radio communications systems are commonly employed to provide voice and data communications to a plurality of mobile telephones or subscribers. Analog cellular systems, such as designated AMPS, TACS, E-TACS and NMT have been deployed successfully throughout the world. More recently, digital cellular systems, such as designated IS-54B in North America and the pan-European GSM system as well PDC and DECT cellular systems, have been introduced. These systems, and others, are described, for example, in the book titled Cellular Radio Systems by Balston, et al., published by Artech House, Norwood, Mass., 1993.
A cellular radio communications system generally includes one or more stations or units, typically referred to as cellular telephones, one or more base stations and a mobile telephone switching office. A typical cellular radio communications system may include hundreds of base stations, thousands of cellular telephones and more than one mobile telephone switching office. The mobile telephone switching office and the plurality of base stations associated therewith generally define the cellular radio network.
The cellular radio network is typically divided into cells which include one base station and the cellular telephones with which the base station is in communication. Each cell will have allocated to it one or more voice channels and, if the cellular radio network is digital, one or more dedicated digital control channels. For example, a typical cell of a GSM digital cellular radio network has one digital control channel and 21 voice/data or traffic, channels. The digital control channel is a dedicated channel for transmitting cell identification and paging information while the voice channels carry the voice and data information. Note that "channel" may refer to a specific carrier frequency in an analog system or to a specific carrier/slot combination in a hybrid TDMA/FDMA system, such as IS-54B or in GSM.
The mobile telephone switching office is a central coordinating element of the overall cellular radio network. The mobile telephone switching office typically includes a cellular processor and a cellular switch which provides the interface to an associated public switched telephone network. The mobile telephone switching office may also include a Home Location Register. The Home Location Register includes a memory device for storing data relating to the subscribers to the cellular system. This data may include the location of the subscriber as well as any specific services requested by the subscriber, such as call waiting or call hold.
Each base station of a cellular radio network generally includes a control unit and an antenna tower. The control unit comprises the base station electronics including the radio control group, the exchange radio interface, a primary power supply for converting electric power from the AC grid to power the individual components within the base station, and a backup power supply. The exchange radio interface of the control unit of the base station electronics provides signals between the mobile telephone switching office and the base station. For example, the exchange radio interface receives data from the radio channel group and transfers the data to the mobile telephone switching office via a dedicated communications link. In the reverse direction, the exchange radio interface receives data from the mobile telephone switching office into the radio channel group for subsequent transmission to a cellular telephone.
The radio control group includes the electronic equipment necessary to effect radio communications. A radio control group typically includes one transmit/receive module for each voice and control channel as well as one signal strength receiver. Each transmit/receive module includes a transmitter, receiver and control unit. The transmit/receive modules are not typically frequency agile and operate, instead, on only one predetermined channel. Control signals from the exchange radio interface are received by the individual control units of the transmit/receive modules. In addition, voice and data traffic signals from the transmit/receive modules are routed over separate interfaces to the exchange radio interface.
Thereafter, each individual transmitter for control and voice signals is connected to a transmit combiner. The transmit combiner combines all of the input signals onto a signal output coupled through a coaxial cable to the transmit antenna. On the receive side, each of two receive antennas is typically coupled to a respective receive combiner where the signals received are separated according to frequency and passed on to the individual receivers in each of the transmit/receive modules.
The base station handles the radio communication with the cellular telephones. In this capacity, the base station functions chiefly as a relay station for data and voice signals. The base station also supervises the quality of the communications link and monitors or receives signals from the cellular telephones. A typical base station is Model No. RBS882 manufactured by Ericsson Telecom AB Stockholm, Sweden for the GSM digital cellular system. A full description of this analog cellular network is provided in Publication No. EN/LZT 101 908 R2B, published by Ericsson Telecom AB.
Through the cellular radio network, a duplex radio communications signal may be established between two cellular telephones or, between a cellular telephone and a landline telephone. In particular, a communications signal is established by a cellular radio communications system, between two cellular telephones, via a voice channel which is established between the two cellular telephones and the cellular radio network. Upon establishment of a voice channel, the microphone and speaker of the cellular telephone are opened or activated to establish voice communications. Alternatively, a communications signal is established between a cellular telephone and a landline telephone via a voice channel between the cellular telephone, the cellular radio network, an associated public switched telephone network and a telephone associated with the public switched telephone network, such as a landline telephone.
A feature node may also be associated with the mobile telephone switching office of the cellular radio communications system or with another communications network, such as a public switched telephone network. For example, the feature node may be incorporated within or otherwise associated with the Home Location Register of the mobile telephone switching office. Even if the feature node is associated with another communications network, such as a public switched telephone network, the cellular radio network may access the feature node via the interconnection between the mobile telephone switching office of the cellular radio network and the other communication network.
The feature node provides predetermined functions to the cellular telephones or to the telephones associated with the communications network with which the feature node is associated, such as a public switched telephone network. The predetermined functions include, for example, establishing an efficient communications link between telephones, such as via intermediate base stations, or providing voice-control speech information and number translation services as well as facilitating the establishment of conference telephone calls. Still further, a feature node may provide paging services for the user of a cellular telephone and may facilitate the establishment of alternative communications links if the primary communications link is unavailable. For example, a feature node is described in more detail in U.S. patent application Ser. No. 08/561,113 entitled "A Method of Establishing Cooperation With a Functionality" and U.S. Pat. No. 5,539,813, both of which were filed on Feb. 16, 1993 and both of which are incorporated herein by reference.
When a source telephone, such as a cellular telephone or a landline telephone, requests communications with a cellular telephone of a cellular radio communication system, the source telephone and the requested cellular telephone generally perform a predetermined handshaking or verification sequence. The handshaking sequence between the source telephone and the requested cellular telephone is supported by the cellular radio network which individually communicates with both the source telephone and the cellular telephone. Since the handshaking sequence is conventional, it will not be described in detail as it is well known to those skilled in the art.
According to the predetermined handshaking sequence, predefined signals are exchanged between the cellular telephone and the source telephone. For example, the handshaking sequence typically determines if the requested cellular telephone is activated, i.e., if the cellular telephone is turned "on." In addition, the user of the source telephone is generally notified by the handshaking sequence if the cellular telephone is already in use, such as by an audible busy signal. However, a voice channel is not established between the source telephone and the cellular telephone during the handshaking sequence.
If the cellular telephone is activated and is not already in use, the cellular telephone alerts the user, such as by an audible ringing or buzzing sound emitted by the cellular telephone, upon notification of the pending request for communications. Once alerted of a pending request for communications, the user of the cellular telephone, if in the vicinity, may either accept the requested communications, such as by answering the cellular telephone by taking the cellular telephone off-hook, or may ignore the alerting signal.
If the user of the requested cellular telephone answers the request for communications, a voice channel is opened between the source telephone and the cellular telephone. The speaker and microphone of the cellular telephone are also opened or activated. Thus, voice communications are enabled or established, via the opened voice channel, between the cellular telephone and the source telephone in each instance in which the user of the cellular telephone answers the request for communications and a voice channel is opened with the source telephone.
For example, even in instances in which the user of the source telephone only desires to transmit data or a message to a cellular telephone, the speaker and microphone of a conventional cellular telephone of an analog cellular radio network will be opened when the user of the cellular telephone answers the request for communications. Thus, in such instances, voice communications will be unnecessarily established between the source telephone and a conventional cellular telephone.
The user of the cellular telephone is oftentimes in the midst of another important activity, such as driving a vehicle or conversing with another person, when the alerting signal announcing a pending request for communications is emitted. Thus, the user's response to the alert emitted by the cellular telephone, such as by answering the request for communications and conversing with the user of the requesting source telephone, will significantly disrupt the user's present activities. Therefore, a user of a cellular telephone generally only desires to respond to certain higher priority ones of the requests for communications while not responding, at least immediately, to the remaining lower priority requests for communications.
Users of cellular telephones have not generally been able to learn the identity of the source telephone, such as the telephone number assigned to or name associated with the source telephone, without responding to the request and commencing voice communications with the source telephone. Therefore, without responding to the alert of the cellular telephone, users of cellular telephones have not been able to discern if the request was of a relatively high priority to which they desire to respond or if the request was of a relatively low priority to which they do not presently desire to respond.
Instead of either responding to or ignoring the request for communications, the user of the requested cellular telephone would, in some instances, rather transfer the request. By transferring the request, a communications link or voice channel is established between the requesting source telephone and another telephone or an automated answering device, such as an answering machine or an automated voice mail system. However, the user of the requested cellular telephone is not provided the identity of the source telephone. Thus, users must first interrupt their present activities and respond to the request, such as by answering the cellular telephone, prior to transferring the request. Accordingly, cellular telephone users are presently unable to selectively decide, based upon the identity of the source telephone, whether to accept, reject or transfer the request for communications and, if transferred, to decide to which telephone or automated answering device the request for communications should be transferred.